1. Field of the Invention
The invention is related to a one-piece medical prosthesis implantable in an anatomical duct in order to treat a disease of said duct.
2. Description of the Related Art
The prosthesis has a longitudinal axis a first radially restricted state or a second radially expanded state and a proximal end and a distal end.
Such a prosthesis is also called a xe2x80x9cstentxe2x80x9d.
On FIG. 1, an example of such a prosthesis is shown as an example of prior art stent.
On this FIG. 1, a portion of a tubular wall structure of a medical intravascular prosthesis 1 is illustrated in a flat expanded view.
This illustration shows said structure as shaped when the prosthesis is in its radially expanded state. The axis 3 materializes the longitudinal direction of the prosthesis around which the prosthesis extends along a cylinder tube.
It can be noticed at 5 that a section of said structure extends near and substantially parallel to another section 7, in the way of a double thread line. This particularity can be seen in different zones such as those referenced A and B on said figure.
This doubling is an inconvenient insofar as meanders substantially xe2x80x9czigzagxe2x80x9d-shaped, such as 9a, 9b, and 9c, look xe2x80x9cwarpedxe2x80x9d. In other words, in its expanded state, the structure of said prosthesis shows a non-regular aspect. In addition, existence of sections 5 and 7 leads to a rigidity of the upper part of the stent at about these xe2x80x9cdoubled sectionsxe2x80x9d. The global balance of the prosthesis may suffer therefrom. The warping implied by this xe2x80x9cdoublingxe2x80x9d on the cells 8 of the prosthesis may affect both the reliability of the opening, the mechanical characteristics and even the efficiency of the prosthesis as a whole.
For bringing a solution to this problem and improving the global quality of the prosthesis, the invention points out modifications which may be set out in three different ways which have in common to solve the above-mentioned drawbacks.
First, it can be stated that the invention points out to modify the above-described prosthesis so that it shows:
first structural elements having meanders extending along a series of parallel helices coiled around the longitudinal axis of the prosthesis, said meanders having apices alternately directed towards the proximal end and the distal end,
second structural discrete elements extending along a series of parallel lines perpendicular to the longitudinal axis, the second structural discrete elements being individually arranged between two adjacent first structural elements and defining connecting struts by intersecting said two adjacent first structural elements,
some of said second structural discrete elements showing either changes of slope with at least one shoulder, but no apices, or apices, but no shoulders,
the second elements of a same line being preferably angularly shifted from the second elements of an adjacent line.
Another way to set out the main solution of the invention is to point out that the openings provided in the essentially cylindrical wall of the prosthesis are essentially xe2x80x9cZxe2x80x9d-shaped both in the first state and the second state of the prosthesis and, at least in the expanded state, peripherally defined by eight apices where the cylindrical wall shows reversing of slope (or a xe2x80x9cturning backxe2x80x9d in the way for example of the apex of a zigzag).
A third way to set out said solution is to mention that the prosthesis of the invention has:
first structural elements having meanders extending essentially perpendicular to the axis of the implant, the first structural meanders having apices with reversings of slope alternately directed towards the proximal end and the distal end, two successive apices being connected together by connecting intermediate lengths so that the first structural meanders define a series of meandering cylinders staggered along the axis of the prosthesis,
second and third structural discrete elements connecting two adjacent staggered meandering cylinders together, the second connecting structural discrete elements intersecting said adjacent staggered meandering cylinders at apices thereof, whereas the third connecting structural discrete elements intersect two adjacent staggered meandering cylinders at connecting intermediate lengths thereof.
In connection with said first and third ways of setting out the solution of the invention, it is advised:
that the second structural discrete elements which have points of reversing of slope, but no shoulders, intersect the adjacent first structural elements (or adjacent staggered meandering cylinders) at the apices thereof,
whereas on the contrary, the third structural discrete elements which have at least one shoulder, but no reversings of slope, will advantageously intersect the first structural elements (or staggered meandering cylinders) at the intermediate lengths thereof, between two apices.
In connection with the above-mentioned problems, it will be noted that another characteristic of the invention advises that the second structural discrete elements, i.e. the second structural discrete elements substantially xe2x80x9czigzagxe2x80x9d-shaped (having apices, but no shoulders) extend between adjacent first structural elements (or adjacent staggered meandering cylinders) over at least a portion of the height (or width) thereof, said characteristic allowing to control the size of the cells of the prosthesis, in particular in the radially open state of the prosthesis.